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.. include:: ../../common.defs

.. _session-protocol:

Session Protocol
****************

|TS| supports some session level protocols in place of or on top of HTTP. These
can be provided by a plugin (see :ref:`developer-plugins-new-protocol-plugins`)
or be one that is supported directly by |TS|.

Session protocols are specified by explicit names:

*  ``http/0.9``
*  ``http/1.0``
*  ``http/1.1``
*  ``http/2``

The session protocols supported on a proxy port are a subset of these values.
For convenience some pseudo-values are defined in terms of these fundamental
protocols:

*  ``http`` means ``http/0.9``, ``http/1.0``, and ``http/1.1``
*  ``http2`` means ``http/2``

Each proxy port can be configured in :ts:cv:`proxy.config.http.server_ports`
to support a subset of these session protocols. For TLS enabled connections this
configuration controls which protocols are offered by ALPN and NPN. Protocol sniffing is
use for non-TLS proxy ports to determine which protocol is being used by the
client. If the detected protocol is not supported for that proxy port the
connection is dropped.

Support for NPN is deprecated, and it will be removed on a future release.
